Over the last couple of months, I've noticed that my red and black plakat has been developing these light patches. It started as a light patch on his sides, then progressed to two spots on his cheeks and a thin strip on his ventral fin, but has now grown to encompass an arch over the top of his head, spots on his caudal fin, and now both of his pectorals. The spots on his fins were white at first, but now many of them are totally clear.
It doesn't seem to be fungal or bacterial, as it's not "fluffy" and there's been no changes to his behavior; rather, his scales and fins just seem to be losing pigment, just like the human dermal condition vitiligo. A friend of mine who used to breed bettas suggested that he might have a marbling gene. I'll be a bit disappointed if that's the case, because I just adored his coloring, but it's definitely fun to see!
Some "before" shots:
Today (July 10):